Just to make sure I did this right:

I put the angle finder on the DS near the rear and had +3
I put the angle finder on the flat spot of the TA on the dif and had -2.

This gives me a true pinion angle of -1, correct?

Front suspension is on the ground and the rear was held up at the dif with a jack. Oh, the rear sway bar was not in it's normal loaded suspension position. Will that be an issue?

 

Sounds to me more like your driveshaft slopes downward from front to rear by 3°; and the rear end slopes upward from front to rear by 2°. Meaning, there's 5° between them. Which is about 3½° or maybe 4° more than you really want.

Sway bar doesn't matter since it doesn't affect ride height. The rest is OK.

 

Just re-did the math. I typed in the wrong values. I'm subtracting the DS angle from the dif angle and now coming up with -4.8.

 

The general idea is, you want the pinion pointed about 1° or so below the drive shaft, such that when torque is applied and the rear rotates the pinion upwards, it comes as close as possible to lining up with the drive shaft. Figure the rear rotates a degree or so as the bushings compress, that's close enough for a typical street car on street tires.

 

Okay. Makes sense.
I just re-did everything and have:

DS -2
Dif -3

Gives me -1.

I'm not exactly "mildly modified" but it will be mostly a daily driver. Is my math correct and a good place to start?

 

Yup. Much better. Should be a good start. Frankly, I doubt you'll find a need to change it. At least, mine has been left about like that the whole time I've had it. Actually I should say, the whole time I've had both of them... I had a T-5 one for several years at that -1° setting, and then I got a T-56 one and set it the same and it works fine like that too.

 

Beautiful!
Thanks for the help.
Now all that's left to do is re-route my TV cable, final set the valves, and put on the VC's.
5 months on the operating table and I finally see the light.

 

No, No, No- stop what you are doing. You do NOT line the pinion off the driveshaft!!!!!!!!! This subject is an age old problem here on TGO, I see thesame bad info given time and time again.


You line the pinion angle off the trans output shaft angle (MATCH them)- THEN go 1* downward on the pinon angle so under thrust the pinion rotates up to 0* line with the output shaft angle and alleviates bad harmonics under throttle.


The driveshaft will still be angled off the output shaft and angled into the pinon. You NEED at least 1* angle on these for the needle bearings inside the u-joints to rotate properly. They will not rotate at less than 1* difference in angle from the driveshaft at either end. This part of the equation really is not important since you could not lower the car enough for this to be a problem where everything is in a straignt 0* line from the output shaft clear to the pinion- so don't worry about this. Just do what I listed in the first paragraph.

 

Here are two old diagrams I posted on here years ago. These wil help you. The middle example of the second diagram show the trans to driveshaft angle as 0*, that one shows the bad example if the driveshaft is in line less than 1* on a u-joint. Thats where the needle bearings in a u-joint will not rotate correctly and cause premature failure.


https://www.thirdgen.org/forums/atta...nion-angle.jpg

https://www.thirdgen.org/forums/atta...on-angle-2.jpg

 

I dont know if I did mine wrong, but I got -5 on the top of the torque arm, and 4- on the driveshaft

I did mine with front wheels on ramps, and the back axle on jack stands.

Although, I wouldnt take advice on it though, I probally didnt do it right.

 

Alright. Until this debate is settled the car will remain parked in the garage.

In Spohn's directions it states: "Using an angle finder place it on the driveshaft (a flat smooth spot) and record the angle indicated."
Next, place the angle finder on the flat surface where the torque arm mounts to the rear end (this surface is parallel with the pinion shaft) and record the angle indicated.

Subtract the pinion angle from the driveshaft angle. The result is "TRUE Pinion Angle".
In order to apply preload you need negative TRUE pinion angle. Adjust the torque arm so that the front of the pinion goes down; continue to check each angle until the pinion angle is more degrees down than the driveshaft angle.


Who's correct?

 

They are both correct (Mine and Spohns). Steve tells you how to get the rear angle but he does NOT tell you what angle.


I am telling you how to find the front (output shaft) angle so you can know what real true angle to set on the pinion. Every car is different based on ride height and driveshaft angle as a by product. Different trans xmembers, bushings, and or shims can alter your front angle. SO concequently, your front angle and rear angle have to cancel each other of you will get bad harmonics occuring if it is out of wack enough (aka- the waa-waa's). It may not happen right away but even being at 2* can wear the u-joints and cause bad harmonic vibrations.


I recall speaking to Steve Spohn a few years back about his subject because it is a tricky one for most people. Steve and I had several phone conversations and emails pertaining to designing new parts back then and other topics came up also.


Viprklr, if its any conselation, I will also bring out my trump card and just tell you flat out I think I am the only guy on these boards that owns vehicles with not just one but two very expensive and exotic full carbon fiber driveshafts. I also happen to be a suspension expert and currently hold a NASCAR license as an active drewchief on a Craftsman style supertruck. Trust me, go off my diagrams. I know custom drivetrains and have them in my everyday llife.

Now this subject is not a critical as people suspect. Its not like something is going to break something else and a mistake is going to be real bad- no- It is just that the more it is off, the quicker the u-joint will wear. THis also is directly related to how much HP you lay down, and/or also how fast of critical speed does that drive shaft spin. The hiogher each of these, the more critical you need the percise pinon angle for reliability.


Conclusion- Now if you go back and re-read my postings above and look at my diagrams, I not only gave you advise, but I ALSO gave the reason WAY it is set that way. A word to everyone else, when giving helpful advise to someone else when it comes to suspension adjustments- always try to arm the person asking with an eduction as to the boundries of that perticular setup- If you can't do that then 1) they still do not learn what it is and are merely setting it because You just said it should be that way, and 2)you many be giving bad info you had heard the same way in the past. We are all here to learn and help eachother. We are not here just to be the quickest to answer. So thel them this or that but tell them WHY so they learn and can use that info to also make an educated judgement for their own- since after all, its not your pocketbook that is affected if the set something incorrectly off of your suggestion and it wears out prematurely.


Now to Sofakingdom, If this had been my $1200 carbon fiber driveshaft that I bought and put into my lets say 600hp car, and I set that Spohn TA pinion angle like you suggested and I genaded a u-joint off the line and it come spinning out of there and brooms into disentigration, Whos *** is on the line for giving me the wrong info. That can happen here- don't let it be you next time. Now unfortunately, someone with that kind of car should know enough about not toi be asking a question like that around a website and should have that kind of knowledge on setup far before accusition of such expensive pacakges- but I have seen it asked and I have seen what sometimes appears to be 14 year old kids giving a 50 year old man advise with the older but not wiser not being aware of such being a new member.

 

Well, I'm a 40 something guy too, but I'll choose to stay out of the controversy just to ask a question since I plan to purchase an adjustable TQ arm in the very near future...so feel free to correct me.

If you place the angle finder say, on the oil pan rail which should be crankshaft centerline...shouldn't that be roughly the the trans output shaft angle too?

 

Confuzed, That will work also if the pan is off. Going against the pan bottom though can be very inaccurate if the pan has seen better days. The lips are uneven and the tranny pan center is usually concaved from supporting the trabs with bloks and such to get the cross member off. If draining the fluid to get the pan off is not a problem then simply gauge the trans angle level at the gasket surface. If the pan is on, then gauging the output height and then tail shaft removal fo the 4 bolts and VSS is quickest. You can do this before you replace the drivesaft just after installing the new TA.


Basicaly what ever creative whay you can gauge the trans centerline angle is fine and then set the pinion angle down 1* from the trans centerline angle. Your done- that simple. Good luck to all. Now if the car is getting in upwards of 500 hp, you will start getting into the 2* range but this is really also based on deflection of bushings and several other suspension setting factors, and mainly if it is now only being used for drag racing only. Top fuel cars can have in excess sometimes of 5* down due to massive HP and thrust, The do not ever see freeway cruising speeds though.

 

Okay. I tried your way Tidbit and came up with the same exact number, -1, as Spohn's way. Did I get lucky or is something wrong?